1. Department of Algebra and Mathematical AnalysisBohdan Khmelnytsky National University of Cherkasy Cherkasy Ukraine
2. LAMIH, CNRS UMR 8201Hauts‐de‐France Polytechnic University Valenciennes France
3. LAMAV, FR CNRS 2956Hauts‐de‐France Polytechnic University Valenciennes France